President Obama dedicated the new September 11 museum during an emotional ceremony that moved attendees to tears Thursday morning, calling the underground memorial a “sacred place of healing and hope” to recover from the nation’s worst terrorist attack.

President Obama and former Mayor Michael Bloomberg stand near a damaged Ladder 3 fire truck as Obama tours the National September 11 Memorial Museum.Photo: Reuters

Standing in front of the famed World Trade Center slurry wall, Obama told a somber group of survivors, victims’ relatives and first responders: “Like the great wall and bedrock that embrace us today, nothing can ever break us.”

“Nothing can change who we are as Americans,” he said.

Before his speech, the president and First Lady Michelle Obama toured the exhibits, which include a mangled fire truck and a memorial wall with photos of victims.

People attend the opening ceremony for the National September 11 Memorial Museum.Photo: Getty Images

“I think all who come here will find it to be a profound and moving experience,” he said.

Obama also hailed the heroes who emerged from the al Qaeda attacks that felled the Twin Towers and damaged the Pentagon.

He cited the rescue and recovery workers who rushed to Ground Zero, the passengers and crew who stormed a hijacked plane’s cockpit over the Pennsylvania field where it crashed, and the military members “who have served with honor in more than a decade of war” since then.

Obama paid special tribute to Welles Crowther, who wore a red bandanna over his face as he helped lead people out of the World Trade Center’s south tower before it collapsed, killing him and hundreds more.

The red bandanna like the one worn by Welles Crowther, who was killed in the attacks.Photo: Chad Rachman

“Welles was just 24 years old, with a broad smile and a bright future,” Obama said.

Obama yields the podium to Alison Crowther (center) and Ling Young during the dedication ceremony.Photo: Getty Images

“He worked in finance, but he had also been a volunteer firefighter, and … he spent his last moments saving lives.”

Crowther’s mom, Alison Crowther, walked on stage with one of the women he rescued, Ling Young, whose sleeveless dress showed off burns she suffered on her right arm.

“It was very hard for me to come here today, but I wanted to come and say, ‘Thank you,'” Young said.

Alison said her son “believed that we are all connected as one family, that we’re all here to look out and care for one another.”

She also said she recognized her son in news accounts of the kerchief-clad hero, saying he had carried a red bandanna with him since childhood — and that she donated one for an exhibit to inspire visitors to follow his example.

“That is the true legacy of Sept. 11,” she said.

Former Mayor Mike Bloomberg, who introduced Obama, said the museum would “stand alongside the fields of Gettysburg, the waters of Pearl Harbor and the Vietnam Veterans Memorial” in honoring acts of courage and compassion.

“Walking through this museum can be difficult at times, but it is impossible to leave without being inspired,” he said.

The museum opens to the public on May 21.

New York firefighters who were trapped in the north tower during the attacks stand on stage during the dedication.Photo: EPA

A firefighter is rescued shortly after both towers collapsed.Photo: AP

Retired Fire Department Lt. Mickey Cross described being trapped for hours with 13 other firefighters and cops in the wreckage of the north tower — and then joining the recovery effort after being rescued.

“There was a real sense of caring for each other,” he said.

Ada Dolch, a school principal whose sister died at the trade center, recalled turning her grief into inspiration to open a school in Afghanistan.

“What a kick in the head to Osama bin Laden!” she said.

Kayla Bergeron remembered walking down 68 flights of stairs in the north tower, amid confusion and fear that there was no way out.

Her final 38 steps to safety were on an outdoor stairway, which was painstakingly removed from the site and installed between the stairs and escalator to the museum’s lowest level.

“Today, when I think about those stairs, what they represent to me is resiliency,” she said.

The “Survivors’ Staircase”Photo: Jin Lee

Mayor Bill de Blasio, who took part in the ceremony, called it “very moving” afterward, and said the museum was a reminder of both the victims who died and the heroes who responded.

“I would say to every New Yorker: It’s someplace you have to visit, you have to experience,” he said.

“It becomes very personal. They did an amazing job respectfully presenting what happened.”

Former Mayor Rudy Giuliani — who became known as “America’s mayor” for his handling of the crisis — said: “It was very hard not to feel very sad.”

“It got you to focus on the life-affirming parts of it,” he said.

“When you’re back in there, it feels like it was yesterday. The emotions come back pretty strong.”

Before the ceremony, Obama walked quietly through an expansive hall with the first lady, Bloomberg, former President Bill Clinton and former Secretary of State Hillary Clinton following behind them.

Museum dedication honors loss and heroism on Sept. 11

It looks like an abstract sculpture, a disquieting artistic piece reminding museum visitors of the carnage. But this “impact steel” was part of the facade of the north tower, and was located at the point of impact where hijacked Flight 11 pierced the building between floors 93 and 99. The jet was carrying 10,000 gallons of fuel and was traveling at about 465 mph when it hit the tower.

Jin Lee

Jin Lee

An elevator motor from the north tower, the largest model in the world when installed, powered one of the express or service cars. For many World Trade Center workers, the decision to take the elevator meant the difference between life and death, as they became trapped when the power failed.

Jin Lee

A piece of one of the hijacked airplanes brings to life the horror of the attacks. In all, 76 passengers and 11 crew members aboard American Airlines Flight 11, a Boeing 767, perished when the jet crashed into the north tower at 8:46 a.m. on Tuesday, Sept. 11, 2001. And 51 passengers and nine crew members died when United Airlines Flight 175, also a 767, slammed into the south tower at 9:03 a.m. Both flights had departed that morning from Logan International Airport in Boston and were on their way to Los Angeles when they were hijacked by al Qaeda terrorists.

Jin Lee

The “Survivors’ Staircase”

Jin Lee

Jin Lee

The symbolic “Last Column,” a steel beam from one of the World Trade Center towers, stands near the slurry wall that held back the Hudson River from the site. The slurry walls formed “the bathtub,” a skewed rectangle with sides about 980 by 520 feet and as deep as seven stories. The wall withstood the forces of tons of collapsing debris and held in place, preventing the waters of the Hudson from flooding lower Manhattan and the PATH train tunnels after the attacks.

Jin Lee

Jin Lee

Jin Lee

This American flag, like several others found in the rubble, gives testament to New Yorkers’ patriotic spirit.

AFP/Getty Images

Getty Images

EPA

Jin Lee

Jin Lee

Jin Lee

Jin Lee

This 20-foot section of twisted metal was once part of the 360-foot transmission tower that stood atop the north tower. The tower supported 10 main television antennas, numerous auxiliary antennas and a master FM antenna. Transmission began in June 1980. Ten TV stations, including all major networks, broadcast from the mast.

Jin Lee

Jin Lee

Firefighter Christian Waugh was among the rescue workers who recovered the body of Fire Department Chaplain Father Mychal Judge. The helmet Waugh wore that day is on display at the museum.

AFP/Getty Images

Getty Images

On display is a standard-issue FDNY shirt that had been worn by Lt. Mickey Kross, one of 16 people who survived the north-tower collapse in a small air pocket under Stairwell B.

Getty Images

Prayer cards, patches and mementos of would-be rescuers who gave their lives at Ground Zero fill a glass display case at the museum.

Getty Images

EPA

A display of missing-persons fliers recalls the anguished days and weeks after all the 9/11 attacks. The signs became part of the urban landscape near Ground Zero and were a heartbreaking reminder of the thousands of metropolitan-area residents who perished.

Getty Images

Injured survivors struggled for years after the attack. One, a burn victim, donated a recovery mask.

Getty Images

A simple pair of eyeglasses and its case are reminders of how lives were changed that day.

Getty Images

These were simple objects on someone’s desk before a jet crashed into the tower: a phone, a Rolodex and a pair of scissors.

Getty Images

Victim Glenn J. Winuk’s ID was found amid the rubble in the days after 9/11. Winuk, 40, a volunteer firefighter in Jericho, LI, was a partner at the law firm Holland & Knight on the corner of Broadway and Dey Street. His partial remains were found near the south tower.

Getty Images

Curators preserved the interior of Chelsea Jeans, including the ash-covered merchandise that owner David Cohen left undisturbed. The clothing store, which was located a block from the towers on Broadway near Fulton Street, became a makeshift shrine and a place of pilgrimage after the Sept. 11 attacks.

Jin Lee

Dust, ash and debris from the collapsed Twin Towers cover the clothes from the Chelsea Jeans store.

Getty Images

EPA

Jin Lee

An American Airlines slipper recovered from the hijacked planes.

AP

Jin Lee

Architectural firm Minoru ­Yamasaki Associates built three large-scale models of the WTC for the Port Authority. This one, built from 1969 to 1971, is the largest and most detailed of the original series of presentation models that survive.

Jin Lee

Getty Images

Former New York City Mayor Rudolph Giuliani looks over a display.

EPA

The countdown to Osama bin Laden’s capture finally ended in May 2011, when Navy SEAL Team 6 killed him in Pakistan.

Getty Images

The hijackers of the four jets are on display, putting faces to the evil that brought death and destruction.

Getty Images

Osama bin Laden is finally dead. But the plot he masterminded will haunt victims’ families forever.

Getty Images

“I can hear you! I can hear you! The rest of the world hears you! And the people — and the people who knocked these buildings down will hear all of us soon!” President George W. Bush used this bullhorn to reassure rescuers — and America.

Share this:

“Our loved ones, including my son, were pulled out of that pit of doom and destruction, and now they want to put them back in that pit where they were massacred,” she said.

“They don’t belong there. My son does not belong in the basement of a museum.”

She added: “Burial of the dead is a very sacred act and this is sacrilegious and really goes against the principle of all religions to have these remains inside a museum.”

New Jersey Gov. Chris Christie, among the officials in attendance, avoided a potentially awkward moment tied to the unfolding “Bridgegate” scandal when organizers scrapped plans to have him speak following a performance of the classic song “Bridge Over Troubled Water.”

Just before the ceremony, a spokeswoman said that singer Idina Menzel was sick.

She was replaced by fellow Broadway singer and Sept. 11 widow LaChanze, who sang “Amazing Grace,” which she dedicated to her late husband, Calvin Joseph Gooding.